Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. Also, the secondary battery has attracted considerable attention as an energy source for electric vehicles and hybrid electric vehicles, which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuel. As a result, the kinds of applications using the secondary battery are being increased owing to the advantages of the secondary battery, and hereafter the secondary battery is expected to be applied to more applications and products than now.
As the kinds of applications and products, to which the secondary battery is applicable, are increased, the kinds of batteries are also increased such that the batteries can provide outputs and capacities suitable for the applications and products. For example, small-sized mobile devices, such as mobile phones, personal digital assistants (PDAs), digital cameras, and laptop computers, use one or several small-sized, light-weight battery cells (unit cells) for each device according to the reduction in size and weight of the corresponding products. On the other hand, middle- or large-sized devices, such as electric bicycles, electric vehicles, and hybrid electric vehicles, use a battery pack having a plurality of unit cells electrically connected with each other because high output and large capacity is necessary for the middle- or large-sized devices.
The middle- or large-sized battery pack includes a plurality of unit cells, which are mounted in a housing (case) having a predetermined size while being electrically connected with each other, and a battery management system (BMS) circuit unit mounted at the inner surface and the outer surface of the case for detecting the voltage, current, and temperature of the unit cells, and therefore, controlling the operation of the battery pack.
In the case that the battery pack is used for electric bicycles, electric vehicles, or hybrid electric vehicles, on the other hand, it is required for the battery pack to have a durability such that in various environments, for example, in a high-humidity condition such as the rainy season and when the battery pack is used for a long period of time.
Especially, the circuit of the BMS is congested, and therefore, the loading density of the element is very high, due to the structure of the compact battery pack. Consequently, when foreign matter, especially moisture, is introduced into the BMS, the circuit and elements of the BMS may be easily corroded due to the moisture. As a result, short circuits of the circuit and elements of the BMS may easily occur, the battery pack may malfunction, and the service life of the battery pack may be greatly reduced. There have been proposed various battery management systems each having a waterproofing member for preventing the malfunction of the battery pack due to the permeation of the moisture. For example, Japanese Patent Application Publication No. 2004-056164 and No. 2001-007547 disclose an O-ring, as a waterproofing member, interposed between a housing body and a cover, constituting a housing, for preventing the permeation of moisture into the battery pack.
However, the technologies for simply interposing the O-ring are limited to be preferably applied to a middle- or large-sized battery pack having a strong possibility of the middle- or large-sized battery pack being exposed to severe conditions. Specifically, O-ring has a strong possibility of the O-ring to be separated from the middle- or large-sized battery pack due to vibration and impact. When the O-ring is separated from the battery pack, much more moisture may permeate into the battery pack through the gap formed due to the separation of the O-ring. Furthermore, micro conductive particles may also be introduced into the battery pack.
Consequently, there is a high necessity for a battery management system that fundamentally solves the above-mentioned problems and is preferably applied to middle- or large-sized battery packs.